1) Field of the Invention
The present invention relates to modified synthetic resins, in which electrolytes (ionic impurities) contained in synthetic resins are fixed in water-insoluble fine particles, thereby preventing the electrolytes from adversely affecting the resins electrical properties and the like, and to a method of modifying the synthetic resins.
The modified synthetic resins containing the water-insoluble fine particles according to this invention exhibit reduced adverse effects caused by corrosive ions introduced from the outside or halogen ions liberated from halogen-containing synthetic resins and are suitable for use as paints, sealing compounds, films, various molded or formed products, etc.
2) Description of the Related Art
Synthetic resins contain electrolytes (ionic impurities) having origin in catalysts used in their polymerization reactions and salts produced secondarily. These synthetic resins are subjected to a process for the removal of the impurities by washing or the like after completion of the polymerization reactions. However, the impurities cannot be perfectly removed, and the electrolytes remain therein in amounts of several tens--several hundreds ppm or in some cases, several thousands ppm in terms of NaCl.
For example, a bisphenol type epoxy resin is synthesized by subjecting bisphenol A and epichlorohydrin to a polymerization reaction in the presence of sodium hydroxide. Sodium chloride produced secondarily by this polymerization reaction remains in the resin an extremely small amount. A polyolefin resin synthesized making use of a Ziegler-Natta catalyst contains a small amount of the catalyst therein. Such a catalyst is an elctrolyte which is soluble in water to ionically dissociate.
These electrolytes in small amounts adversely affect the electrical properties of the synthetic resins and cause films, coatings and other molded or formed products thereof to deteriorate. In addition, when the synthetic resin is used in contact with metals as paints, sealing compounds, additives, films and the like, the electrolytes cause corrosion.
When an epoxy resin, in which a small amount of electrolytes remain, is used in an electro-coating paint by way of example, anodic dissolution is caused by chloride ions. In anionic electrodeposition coating, performance of a coating film is impaired. In cationic electrodeposition coating in which a coating film is formed on a cathode, chloride ions cause the coating device serving as an anode to corrode. Moreover, the presence of alkali cations such as Na.sup.+ causes the cathodic exfoliation of the coating film in the cationic electrodeposition coating. The cathodic delamination causes the coating film to separate under a wet environment. With respect to a coated steel sheet exposed to a seaside environment in particular, scab-like rust extends from its processed or cut parts and coating flaws. It is therefore necessary to prevent the electrolytes from remaining in both anionic and cationic electrodeposition coatings.
When a paint is applied on a metal, the corrosion of the metal occurs from pinholes of the coating film and its edges. The cause is attributed to the fact that electrolytes localize into anions and cations underneath the coating film, thereby causing electrical polarization to form local cells. The electrolytes in this case include corrosive impurity ions, which have entered from the external environment after the coating, other than those remaining in the synthetic resin, said ions greatly affecting the corrosion.
Vinyl chloride resins, fluorine-containing resins, halogen-modified resins and the like are accompanied further by a problem that electrolytes are incorporated therein in the course of their synthesis and at the same time, bound halogen atoms decomposedly liberate therefrom with time to form halogen ions incorporated therein.
In some application fields, the synthetic resins have recently been required to be highly purified. In the field of sealing compounds for semiconductors by way of example, it has been attempted to use super-purified water in washing the synthetic resins after their synthesis. The super-purified water is very expensive, and the electrolytes cannot be eliminated sufficiently by a washing process only.
Although it has been proposed to remove corrosive ions in an electro-coating paint by an ion-exchange resin [Japanese Patent Application Laid-Open No. 173296/1984 and Japanese Patent Application Kohyo (through PCT) No. 501553/1989], recovery and regeneration processes of the ion-exchange resin in the form of particles are complicated.
In addition, it has been proposed to add high-gelatinized cation-exchanger adsorbed with hydrogen ions, which may be partially substituted with heavy metal ions, to an electro-coating paint (Japanese Patent Application Laid-Open No. 65077/1985) or to add a cationic resin adsorbed with the oxo acid anions of a heavy metal to an electro-coating paint (Japanese Patent Application Laid-Open No. 184266/1984). However, conventional ion exchangers have only an insufficient function for fixing the electrolytes because of insufficient purification of such fine particles, and also have only an insufficient effect for reducing the influence of the impurity ions which entered from the external environment.
Attention has been given to particles of an anion exchanger as an improver by which chloride ions in synthetic resins are fixed to render the ions harmless. For example, hydrotalcite particles undergo an ion-exchange reaction to fix anions present in a synthetic resin when they are melted and mixed with the synthetic resin. However, conventional particles having ion-exchange function such as hydrotalcite particles are generally often coagulated. Therefore, their uniformly-dispersing ability is poor and their ion-exchange reactivity is low, so that they exhibit their fixing action for the impurity ions for the first time by their melting and kneading at an elevated temperature.
It has been proposed to prevent filiform corrosion by causing these hydrotalcite particles to contain in a film-forming component (Japanese Patent Application Laid-Open No. 166568/1984). However, this method can cope with filiform corrosion occurring under a relatively dry environment, but cannot prevent the separation of the coating film and the occurrence of scab-like rust under a wet environment. In addition, since the conventional hydrotalcite particles are unpurified fine particles, electrical properties are impaired when their proportion is too great. It is however difficult to suitably determine their proportional conditions.